Maryland Grows

No, I’m not talking about my fellow Master Gardeners here. (Though, hurray, go us!) I’m talking about plants (specifically edible plants) that “volunteer” or spring up unasked in your garden. What are they, how did they get there, are they worth keeping? Your questions answered!

First of all, some definitions. We talk about “volunteers” mostly in the context of vegetable plants. Gardens might also contain “self-seeding annuals” which are flowers like calendula and cosmos that spread their seeds widely at the end of the season, assuring that their offspring will pop up the next year. This can be fun, not to mention a savings on your plant budget, but can also get out of control. In the context of perennials, we call these ultra-spreaders “aggressive” or “invasive” (the latter being restricted to non-native plants) and discourage their use, unless you have a large space you want colonized by aggressive native plants. Perennials can spread either by seed or by roots searching out new areas to grow.

A volunteer tomato, or other annual vegetable, is basically equivalent to those self-seeding annual flowers. Some veggies volunteer more than others, for reasons I’ll get into below. Tomatoes are one of the most prolific, but you’ll also see squash, potatoes, and random other plants volunteering.

They’ll show up where you expect them, and also in totally mysterious places. How did they get there? Well, in several ways.

Seeding from the parent plant

This makes sense. You grow a tomato in a garden bed, and next year there are lots of little tomato seedlings springing up in the same spot. Cherry tomatoes are particularly prone to volunteering, because no matter how hard you try to pick every fruit, some of them fall off and end up buried under mulch or soil. If you don’t clean up continually and thoroughly, seeds will spend the winter in the ground and germinate the following year (usually in late spring or early summer, when the soil warms sufficiently). Tomato seeds are surprisingly tough for warm-weather plants, and will survive freezing.

Other plants prone to drop fruit will also do this, if less frequently, and vegetable plants that form seedheads may create lots of volunteers. (Watch out for amaranth!) Potatoes also fit in this category, although they aren’t spreading seed but rather resprouting from tubers left in the ground. In my experience, you never get every single potato at harvest, and they’re happy to hang out underground and make new plants the next year. Garlic and other alliums do this too.

Seeds in compost

Most home composters have seen plants springing up inside compost bins, especially open ones that don’t get very hot. We’ve learned that unless you want to grow your own avocado plant (transplanted indoors), you don’t put pits into the compost, and we’ve also seen lots of mystery squash and other cucurbits. When we spread the compost on our gardens, we also spread seeds that haven’t been killed by the composting process. You have to get the compost extremely hot to kill tomato seeds, so again, tomatoes are going to be common volunteers.

How do these seeds get into your compost in the first place? Either from garden waste or kitchen waste (or some other random event like windblown seed, pooping birds, or passing helpful strangers). When you clean up your garden in the fall, you might put tomato plants into the compost bin. Is this a good idea? Maybe not, for several reasons. First of all, you could be introducing diseased material that may survive the winter and be reintroduced to the garden next year. Secondly, you’re bringing in seeds. Tomato seeds from overripe, fully ripe, or even immature fruits can germinate. The last may surprise you, but I looked into it after hearing from MG Lesley Furlong, one of the Derwood demo garden composters, that she suspected seeds from green tomatoes added to the compost were causing the abundance of seedlings we’ve seen all over the garden, and found this interesting article linking to research on the topic. Tomatoes in the “mature green” stage (not pale green and hard, but getting close to the “breaker” stage where color begins to appear) can have viable seeds. If you don’t want volunteers, you should keep them out of the compost bin.

Volunteer cucurbits could be from garden waste, but are more likely to be from kitchen waste. In either case, they result from fully mature (or nearly mature) fruits, and therefore are most likely to be from winter squash. Summer squash are eaten at an immature stage where the seeds aren’t yet viable; same with cucumbers. Melons are eaten ripe and so the seeds are viable, but melon seeds aren’t seen as volunteers as often, probably because they aren’t as tough. (I have enough trouble growing melons when I put the seeds in on purpose!)

I’ve also often had potatoes come up in the compost, but they don’t get transferred to the garden since I sieve my compost before using.

Seeds spread by critters

Birds, squirrels, and other animals will remove seeds and fruits from the garden and distribute them, by excretion or sometimes by burying. If you’ve had fruiting plants (again, mostly tomatoes) pop up far away from your vegetable garden and not where you’ve put down compost, this is probably why.

Humans might also be responsible for spreading seeds around. We might eat a fruit and spit the seeds on the ground, or drop part of our harvest. Every Halloween at my house, we put a decorative selection of squash and gourds on the front porch, and then we remove them before the squirrels start gnawing at them and making a mess. Sometimes they’re used in the kitchen, or go straight into the compost, but sometimes we place them under a particular tree so the squirrels can continue munching, and next year mystery cucurbit vines appear.

Are volunteer plants worth keeping?

This is always up to you, the gardener. But here’s some context that might help you decide.

• Do you know what you’re getting? Part one, cross-pollination. All you can really tell from the appearance of the seedling is what species it is—or possibly not even that much. An apparent squash plant, for example, may produce inedible “gourds,” if you threw those into your compost last fall. The fruits sold as decorative gourds are sometimes Cucurbita species (squash, but maybe not edible squash) and sometimes actual gourd species that look just like squash as young plants. Gourds can be edible, but you’d have to figure that out after they’ve grown up and produced fruit. Even if it’s squash, it’s almost certainly a hybrid between two varieties that crossed while growing in a field or in your garden. It may grow up to be the most delicious squash you’ve ever tasted, or it could be bland or bitter; you won’t be able to tell. My best advice would be to only grow out volunteer squash if you are sure of the source; in other words, if you know it’s from a squash you grew yourself that couldn’t have cross-pollinated with a different squash of the same species. Do I follow my own advice? Ha. Where is the adventure in that?
• Part two, children of hybrids. Tomatoes are less likely than squash to cross-pollinate within the garden, so when you plant a saved tomato seed, or let one volunteer in the garden, you’re more likely to get a reproduction of the parent plant. Unless the parent was a hybrid variety, in which case the children will be a weird selection of their grandparent plants, some of which might not be very tasty (because their value to the hybrid came from other characteristics, like disease resistance). Therefore, if a volunteer plant comes up right where you had a tomato growing last year, and you remember what that tomato was, and it wasn’t a hybrid, and it wasn’t growing close to a hybrid that may have flung its seed around, you could let it grow and you may be lucky. (Just for the record, I’ve found (after letting a bunch of volunteer seedlings grow to see what happened) that one of the parents of hybrid cherry tomatoes often turns out to be something like ‘Matt’s Wild Cherry’ that will be huge and prolific with a thousand tasty tiny fruits, so if you like that kind of thing, you might risk letting the mystery plant grow. But don’t blame me if you’re disappointed.)
• Late start. Volunteers often come up late in the season, and even if they have the genes and the drive to grow really fast, they may be late producers. Plants that come up from tubers and bulbs may have less energy available and your harvest may be smaller and later than if you’d used fresh material.
• Location is everything. Ask yourself if you have room for this plant where it has sprung up, or even somewhere else you can transplant it to. Is it going to get really big and shade out another plant, or steal its nutrients? Is it growing in a random spot in your landscape, not fenced and protected from animals that might eat all the fruit off it, or even eat the plant itself? (Those volunteer cucurbits under the tree where I left the pumpkins last year never actually survive.) Is it not part of the plan you carefully made for your garden? Can you deviate from the plan and save this plant? Please, help!…

Um, sorry. There’s something about volunteers that makes us value them even more that the plants we started from seed ourselves or spent money on. Maybe it’s because we admire their tenacity and sneakiness and will to live. It’s probably far more pragmatic to just yank them, but even the most experienced gardeners still sometimes… just let them grow.

You decide.

By Erica Smith, Montgomery County Master Gardener. Read more posts by Erica.